Induction heating apparatus



Oct. 13, 1953 R. P. G. GARDNER INDUCTION HEATING APPARATUS Filed Dec. 18, 1950 4 Sheets-Sheet 1 w kg Oct. 13, 1953 R. P. G. GARDNER 2, 0

INDUCTION HEATING APPARATUS Filed Dec. 18, 1950 4 Sheets-Sheet 2 m Q M Inve tor Oct. 13, 1953 R. P. G. GARDNER 2,655,590

INDUCTION HEATING APPARATUS 7 Filed Dec. 18, 1950 I 4 Sheets-Sheet s Q F/G.6. m

Oct. 13, 1953 R. P. G. GARDNER 2,655,590

INDUCTION HEATING APPARATUS Filed Dec. 18, 1950 4 Sheets-Sheet 4 QUAMQ Inuen or Patented Oct. 13,1953

INDUCTION HEATING APPARATUS Robert Percy Govan Gardner, London, England, assignor to The Ohio Crankshaft Company, Cleveland, Ohio, a corporation of Ohio Application December 18, 1950, Serial No. 201,338 In Great Britain January 4, 1950 17 Claims.

This invention relates to induction heating, and is primarily concerned with the provision of means for temporarily connecting together in an electric circuit conductors for carrying a heavy current. For example the invention may be applicable where it is desired to connect a single inductor alternatively to either of two different generators, or to energise any one of two or more inductors alternatively from a single generator.

the bridging contacts radially outwards into firm contact with the walls of the bores so as to connect the conductors electrically together.

In one form of the present invention induction heating apparatus includes at least two generators electrically connected together in series with an inductor which is intended to be supplied alternatively from one of the generators while the other generators are short-circuited, in which the two supply conductors of at least one of the generators are formed respectively with coaxial bores in adjacent parts and are provided with an expanding plug comprising two or more bridging contacts each formed to lie partly in one bore and partly in the other, and means for expanding the bridging contacts radially outwards into firm contact with the walls of the bores so as to shortcircuit that generator.

In one such arrangement the inductor is provided with two pairs of supply connectors arranged at remote ends of its operative part for electrical connection to the two generators. For example the inductor may be of circular form divided into two semi-circular portions with pairs of connectors at diametrically opposite points.

For some purposes such as hardening gear wheels which have diametral pitch numbers greater than four, it is desirable to apply induction heating in two stages. Thus it has been proposed first to heat a workpiece such as a gear wheel by induction heating at a frequency not greater than 10,000 cycles per second to raise the temperature of the mass of the gear to the region of the Curie point, and then to subject the workpiece to induction heating at a frequency of not less than 100,000 cycles per second to surface harden the teeth themselves, whilst also refining the core of the gear wheel at the same time. In order to ensure a rapid change-over from one stage to the other, the present invention allows the same inductor to be employed for both stages of heat treatment.

For use in such a method the induction heating means referred to above is employed in conjunction with generators of difierent frequencies.

The invention is not, however, limited to arrangements in which the connectors of the two generators are arranged in series and one generator is short-circuited., but may also be applied to what may be termed a parallel arrangement with one generator open-circuited.

Thus according to a further aspect of the invention, induction heating apparatus includes at least two generators electrically connected together in parallel across an inductor which is intended to be supplied alternatively from one of them whilst the other generators are opencircuited, a supply connector from at least one of the generators and from the inductor being formed respectively with coaxial bores in adjacent parts, and an expanding plug is provided comprising two or more bridging contacts each formed to lie, partly in one bore and partly in the other bore and means for expanding the bridging contacts radially outwards into firm contact with the walls of the bores, and for retracting the bridging contacts out of contact with the bores so as to open-circuit that generator.

Nor is the invention limited to changing over an inductor from one generator to another, but it may be employed for connecting one or other of two or more inductors to a single generator. In a manner analogous to the various arrangements referred to above, the apparatus may comprise two or more inductors connected together in series with a single generator and provided with expanding plug arrangements for short-circuiting one or more of the inductors, or alternatively the inductors may be connected in parallel across the generator and be selectively opencircuited.

In any of the arrangements of the present invention referred to above, where rapidity or ease of operation are required the expanding plugs may be solenoid-operated.

In a convenient construction each expanding plug includes a plunger formed with tapered wedging surfaces inclined to its axis which cooperate with corresponding surfaces formed on The invention may be carried into practice ,in.

various ways, but one specific embodiment and various alternative arrangements .willnow be described by way of example with reference to the accompanying drawings, in which Figure 1 is a plan of a dual-frequency, two piece inductor for the heat treatment. of gear wheels with connections shown diagrammatically to alternative sources of electric power,

Figure 2 is a side elevation in section on theline IIII of the inductor of Figure 1,

Figure 3 isa sectional view on an enlarged scale of a typical expanding plug for short circuiting either of the transformers of Figures 1 and 2.

Figure 4 is a plan of the plug of Figure 3,

Figure 5 is a diagram showing a modified arrangement in which a one-piece inductor is employed,

Figure 6 is a diagram showing a further modification in which the sources of power are connected in parallel to the inductor,

Figure is a diagram showing an alternative arrangement in which two inductors are connected alternatively in parallel across a single source of power, and 7 Figure 8 is a diagram showing yet another alternative arrangement in which three inductors are connected in series with a single source of power.

In the embodiment of Figures 1 to 4 a single inductor A is employed for heating a gear wheel first at one frequency from one generator and thereafter at a much higher frequency from another generator. The inductor A is of generally circular form, intended to surround the gear wheel to be hardened, but as shown in Figures 1 and 2 is formed in two separate. semi-circular halves A and A the ends A and A of onehalf A being bent outwardly so as to lie parallel to the ends A and A of the other half A at two diametrically opposite points. The ends A A A and A -are extended at right anglesso as to form end connectors, of which A and A are'connected across the secondary winding of; a radio-frequency transformer B whose primary is supplied from a thermionic radio-frequency generator B while the end connectorsAf and A are connected across the secondary winding of a high-frequency transformer C whose primary is supplied by a rotary high-frequency generator 0. In Figure l the generators B and C and the transformers B and C are indicated purely diagrammatically.

Each of the pairs of end connectors AAA and A A is formed to receive a short-circuiting device constructed to carry the heavy current employed without offering undue impedance, Each such device comprises an expanding plug-D fitting into coaxial bores A formed one in each of the pairs of end connectors, so as tobridge the connectors and short-circuit the transformer secondary to which they are connected. Thenexpanding plug D is formed with three, bridging contacts D having silver plated contact faces D for engaging correspondingly shaped faces forming part of the edges ofthe bores A7, part of the length of each bridging contact passing through the bore in one connector while another part passes through the bore in the adjacent connector. Each bridging contact D extends through a longitudinal slot D formed in the wall of a tubular sleeve D in the manner shown in Figures 2 and 3, the sleeve D providing a fixed support for the-bridging .contacts. The bridging contacts D are in the form of wedge-shaped plates, tapering longitudinally in profile, and the inner parts lie in radial slots D formed in a solid central. plunger D which lies inside the sleeve D As shown-in Figure 3 the inner surfaces D of the slots D? are inclined to the axis of the plunger so. as to correspond with the taper of the bridging contacts D so that when the plunger D is moved axially upwards as shown in Figure 3, the bridging contacts are forced radially outwards by the wedging surfaces into firm contact with the-edges of the bores A" of the two connectors. Ball or roller bearings D may bev interposed between the wedging surfaces of the bridging contacts D and slots D to minimise friction. A pair of beryllium-copper spring rings D -passes through apertures in the three bridging contacts and surrounds the sleeve 1), and urges the three bridging contacts radially inwards, so that when the plunger D is moved axially downwards the bridging contacts .are moved inwardly out of contact with the. two connectors.

Each expanding plug Dmay be operated by means ofa solenoid E acting on the sliding plunger D so that the, plug can be placed incircuit or withdrawn from circuit very quickly; The insertion or withdrawal from circuit takes place in one movement, the insertion into circuit-being effected by'the axial movement, of the central plunger D in one direction, so that the wedging surfaces D force the, inclined bridging contacts D radially outwardsinto contact with the edges of the coaxial bores A7, while. the withdrawalgfrom circuit is effectedby retraction of the central plunger D to release the bridging contacts which are moved radially inwards byqthe spring rings D In the; present arrangement, therefore; the expandingplugs can be employed to cut out alternatively the high-frequency transformerzC and the radio-frequency transformer. B1, and in each case the bridging contacts; D1 as;wellv as short-circuitingone transformer will complete the circuit of the indlllCtOIiAWith respectxto. the other transformer from whichit 1 is being sup.- plied. .It will be understood that. the operator will ensure that before the secondary of either transformer is shcrt-circuited by means of them:- panding plug D, the supply. to its primary from the appropriate generator willfirst be switched off to avoid damage. Various subsidiary or.interlocking contacts may be provided forthi's purpose if desired.

It will be appreciated thattheconstruction described provides a simple. connector for establishing alow-impedance connection betweema pair of, conductors without imposingaany direct mechanical forces uponuthe supports by @which the conductors are carried. Avery; high contact pressure can be employed-soars to allow the passage of the very high currents involved ininduction heating whilst a change of connection can. be performed with great rapidity and simplicity.

In the modified arrangement shown diagrammatically in Figure 5-, the general arrangementof parts is similar to: that. already. described-with 5 reference to Figures 1 to 4 and the same references will be used in relation to similar parts. In this case, however, a one-piece inductor F is employed, of circular form, and having only two end connectors F and F The inductor F is connected in series with the secondaries of the two transformers B and C and the expanding plugs D are employed inan identical manner to that already described to short-circuit one or other 0 the transformers.

In the further modification shown diagrammatically in Figure 6, the one-piece inductor F is connected across the two transformers B and C which are connected together in parallel. In this case the two expanding plugs D are employed drawings.

Figure 7 shows diagrammatically an arrangement in which a single generator B supplies through a single transformer B 'either of two inductors F which are connected in parallel. The

expanding plugs D are employed as switches to connect whichever one of the inductors F is required tobe energised for operation and to disconnect the other from the circuit.

In Figure 8, the arrangement diagrammatically shown is one in which three inductors F are all connected in series with a single source of power B, and expanding plugs D are employed to "short-circuit and thus de-energise whichever of the inductors F are not required to be energised at any moment.

The method of operation of the alternative arrangements shown in Figures 5, 6, 7 and 8 will be obvious from the illustrations and from the earlier part of the specification and will not be further described. As already mentioned the arrangement of the electrical connections is shown purely diagrammatically inFigures 5, 6, 7 and 8, and it will be understood that in practice the length-of all the connections will generally be kept to a minimum.

What I claim as my invention and desire to secure by Letters Patent is:

1. Induction heating apparatus comprising an electric circuit adapted to be connected to a source of alternating current and to carry a heavy current, an inductor in the circuit, a pair of heavy, rigid conductors in the circuit in closespaced, insulated relationship having a pair of coaxial bores formed respectively in adjacent parts of them, an expanding plug adapted to extend into both the bores, and having a plurality of bridging contacts each formed so as to lie partly in one bore and partly in the other bore, and means for expanding the bridging contacts radially outwards into firm contact with the walls of the bores so as to connect the two conductors together.

2. Induction heating apparatus as claimed in claim 1 in which the means for expanding the bridging contacts comprises a plunger movable relatively to the bridging contacts in an axial direction, the plunger being formed with wedging surfaces inclined to the axis and engaging co-operating surfaces formed on the bridging contacts, and in which on axial movement of 6 the plunger in one direction the'wedging surfaces force the bridging contacts radially outwards into firm contact with the walls of the bores. I

3.-Induction heating apparatus as claimed in claim 2 in which the plunger is solenoid-operated. I

4. Induction heating apparatus as claimed in claim 3 in which the bridging contacts lie partly in longitudinal grooves formed radially in the body of the plunger, the bottom surfaces of the grooves being inclined to the plunger axis and comprising the wedging surfaces.

5. Induction heating apparatus as claimed in claim 4 including a tubular sleeve which surrounds the plunger and retains and supports the bridging contacts, the sleeve being formed with apertures through which the bridging contacts extend.

6. Induction heating apparatus as claimed in claim 5 including spring means acting on the bridging contacts to bias them in a radially inward direction.

7. Induction heating apparatus as claimed in claim 6 including rolling bearings interposed between the wedging surfaces of the plunger and of the bridging contacts.

8. Induction heating apparatus including an inductor, at least two alternating current gen- 'erators connected together in series with each other and with the inductor, a pair of conductors connected to the terminals of at least one of the generators and having a pair of coaxial bores formed respectively in adjacent parts of each and an expanding plug associated with the pair of coaxial bores and adapted to extend into both bores, the said plug comprising a plurality of bridging contacts each formed to lie partly in one bore and partly in the other bore, and means for expanding the bridging contacts radially outwards into firm contact with the walls of the bores, whereby the bridging contacts will shortcircuit the associated generator.

9. Induction heating apparatus as claimed in claim 8 in which the generators are of different frequencies.

10. Induction heating apparatus as claimed in claim 9 in which the inductor is provided with two pairs of supply connectors arranged at remote ends of its operative part for electrical connection to the generators.

11. Induction heating apparatus as claimed in claim 10 in which the inductor is of circular form divided into two semi-circular portions, with pairs of connectors at diametrically opposite points.

12. Induction heating apparatus as claimed in claim 11 in which the means for expanding the bridging contacts comprises a solenoid, a plunger movable by the solenoid relatively to the bridging contacts in an axial direction, the plunger being formed with wedging surfaces inclined to its axis and engaging co-operating surfaces formed on the bridging contacts, and in which on axial movement of the plunger in one direction the wedging surfaces force the bridging contacts radially outwards into firm contact with the walls of the bores.

13. Induction heating apparatus comprising an inductor formed of two separate parts spaced apart so as to enclose between them a space for a workpiece, two pair of supply conductors of which each pair is connected to adjacent ends of the two inductor parts, each pair of supply conductors having a pair of coaxial bores formed sQMiQQQ respectively adjacent parts 3 of, the two con;-

ductors,;. a; pair-of alternating current generators of diflerent frequency each; connected in series with one of the pairs of supply conductorss and thusin; series with; the two inductor-93 1 d. an expanding plug associatedwith each pair of; eo,- axial bores and adapted to extend into both bores, in-Whi h ch p n pl c mprisess plurality of bridging-contacts, carried by; the plug and-each :formed to lie partly. in one, bore and partly in the other bore, and means for expanding the-bridging; contacts radially outwards; into firm contact witnthe; wallsofthe boresso as to short-circuitthe, associatedconduc ors and theeencrator con ected BO them}.

' 14;; Inductionheating apparatus as! claimed in claim ;1 3 in, which the ,means for-expanding -the bridging contact compris s apl llger movabl relatively to the bridging contacts in an, axial direction, the plunger being formed. with-;wedging surfaces incl-ined to the axis-and engaging cooperating suri cesjf rme on. nbrideine, ontacts, and in which on axial movement ofi-the plungerin one direction; thet-wedging surfaces forces: the bridging contacts radially-outwards into firm-contact with the walls of the bores.

15. Induction heatingapparatusincluding an inductor, at, least twogenerators of alternating cmtrentior connectiontogether in; parallel across the; inductor, conductors connectedto the terminals or each, generator and conductors connected; to thQinduCtOKtO which a duct r connected ;to at least one f e, e rator rminals and aconductor:connectedfto the inductor are, separatedby a spaceandformed respectively with coaxiaLbor-es in \partsadjacent the space, andanexpanding; plug-associated with the coaxialv bores and. adapted :to extend across. the space into both bores,- thesaid expanding plug comprising, a plurality of bridging; contacts formed to her-partly inoneboreandpartly in the; other boreland means for expanding-the bridging contacts radially outwards intofirm contact with the, walls oi; the-bores, so as to completetheconn ction f hat sen rat nwith the inductor, and for retracting the. bridging contactsloutoivcontact withthe .wallsloin h bores so as to. open-circuit that generator;

16.= Induction heatin pp ratus comprising; an

lte ating, ur n e er r-l at leasttwc inductors connected together in series-with eachother and with the generator, conductors connecting the inductors: vancithe generator, t ethen. the pair oi'conductors-connected to at least one ot the inductors having a pair; of, coaxial bores formed-;respectively in adjacent parts oi; them, anexpandingplug associated with; thepair of coaxial; bores ,and-;adapted to extend into vboth bores, a plurality of bridging contactsforming a part of (theplug and formed tolie partly; in one, bore and, partly in; the other bore angkmeans for expanding-the bridging contacts radially outa s to firm tact w h-the ;W 1s., f...- he bores, whereby thebridgingmontacts will=,5l 1,ort circuit the. associated inductor.

17. Induction heatingapp aratus.--including; an alternating; current generator, a plurality oiindoctors for connectionv togetherinparallel to-the generator to be alternativelysupplied ;by it,; conductors connected to the, terminals ofthe gen erator and; conductors connected to each; in ductor, a conductor connected to thergenergtor and a, conductor connected to at. least one-. of ;the inductors being separated by a space andjormed respectively with coaxial bores in;parts adjacent the space, an expanding plug associated with; the coaxial bores and adaptedtqextend flCljOSEthQ space into the bores, the said-expanding plug comprising a plurality; of -b11idging=contactseach formed to lie 1 artly in; one bere;and;:-P&. C X=' the other bore and means, forexpandingthe bridging contacts radially; outwatdszintonfirm contact with the walls oi the bores; so.- as to completethe connectionnof thatinductor-to the generator, and for retractingv the brid ll xcontactsout of contact with the walls o tl 1 e-;be1 es so as to disconnect that inductor from these!)- erator.

ROBERT PERCY 'GOVAN, GARDNER.

ReferencesCited in the file of this patent.

UNITED :STATES; P.l"1EI-I'-I[S.-

Number Name Date 592,443 Pr-uckneret al. Oct. 26,184! 1,968,869- Austin Aug. 7,1934 2,321,189- Dravneek- June 8,;1943 2,452,365 Frederick-- Oct: 26,-;1848 

